Resid catalyst with high metals capacity

ABSTRACT

A catalyst, and method of preparing and using a catalyst, for the hydrodesulfurization of metal-containing heavy feedstocks, which has improved catalytic life and metals capacity. The catalyst contains Group VIB and Group VIII metals or metal compounds on a support comprising alumina wherein the support has at least 80 percent of said pore volume in pores having a diameter of between 110 and 190 Å and at least 70 percent of said pore volume in pores having a diameter between 130 and 200 Å.

BACKGROUND OF THE INVENTION

The present invention relates to a method for the preparation of acatalyst carrier, to a hydrocarbon desulfurization catalyst preparedusing the carrier, and to a process for hydrodesulfurizing a hydrocarbonfeedstock using the aforementioned catalyst. More particularly, itrelates to a method for the preparation of a porous catalystsubstantially free of macropores (those having diameters above 1000 Å),and containing at least one metal and/or metal compound of Groups VIBand VIII of the elements. Still more particularly, it relates to acatalyst which comprises a predominantly alumina carrier component whichis substantially free of macropores, has a particular micropore sizedistribution, and contains the aforementioned metal and/or metalcompounds. It also relates to a hydrocarbon hydrodesulfurization processusing the catalyst.

The pressing need for desulfurizing hydrocarbon oils obtained frompetroleum processing is well known. When these stocks are combusted as afuel in the usual manner, the sulfur present in the hydrocarbon becomesa serious pollutant of the atmosphere in the form of sulfur oxide gases.

Typical operating conditions for hydrodesulfurization processes includea reaction zone temperature of 600° F. to 900° F., a pressure of 200 to3000 psig, a hydrogen feed rate of 500 to 15000 SCF per barrel of oilfeed, and a catalyst such as nickel or cobalt and molybdenum or tungstenon a porous refractory support.

A problem which has been recognized in the case of hydrodesulfurizationof heavy oils is that if the heavy oil contains organometalliccompounds, the effective catalyst activity tends to decline relativelyrapidly, particularly when the impurity is more than about 10 to 20 ppmmetals such as dissolved nickel and vanadium. These metallic impuritiesare said to deposit on the surface and in the pores of thehydrodesulfurization catalyst.

An approach to this problem of metals impurity deactivation ofhydrodesulfurization catalyst has been to alter the pore structure ofthe catalyst. However, the answer as to what pore structure is best hasnot been easily obtained, and in fact there remains a conflict in theanswer suggested by the prior art. U.S. Pat. Nos. 4,066,574; 4,113,661;and 4,341,625, hereinafter r®ferred to as Tamm '574, Tamm '661, and Tamm'625, the contents of which are incorporated herein by reference as iffully set forth in iosis verbis, have discussed the conflict in the artand suggested a solution.

Tamm's patents disclose that heavy oil feedstocks containing metals,particularly residuum feedstocks, are hydrodesulfurized using a catalystprepared by impregnating Group VIB and Group VIII metals or metalcompounds into a support comprising alumina wherein the support has atleast 70% of its pore volume in pores having a diameter between 80 and150 Å. An especially outstanding hydrodesulfurization catalyst, in termsof very low deactivation rate, is attained by using an alumina supportof the above pore size distribution.

In Tamm '661 the catalyst is prepared by taking a predominantlyalpha-alumina monohydrate, sized in the range below 500 microns, andtreating it with a particular amount of monobasic acid. The acid and theresulting mixture is then at least partially neutralized by admixingwith an aqueous solution of a nitrogen base such as aqueous ammonia. Thesolution contains 0.6 to 1.2 equivalents of base per equivalent of acid.The treated and neutralized product is converted into a catalyst carrierby shaping as desired, drying, and calcining. Finally, the catalystsupport is impregnated with the aforementioned metals.

It would be advantageous if the catalysts and processes of Tamm '574,'661 and '625 could be improved by imparting greater life to thecatalyst in resid processing service.

SUMMARY OF THE INVENTION

According to the present invention, a process is provided forhydrodesulfurizing a hydrocarbon feedstock containing metals whichcomprises contacting the feedstock under hydrodesulfurization conditionswith a catalyst prepared by impregnating Group VIB and Group VIII metalsor metal compounds into a support comprising alumina wherein the supporthas at least 70 volume percent of its pore volume in pores having adiameter of between 110 and 190 Å. The total pore volume of the supportis in the range of from about 0.5 to about 1.1 cubic centimeters pergram, less than 5% of said pore volume is in pores having a diameterabove 500 Å, and less than 2% of the pore volume is in pores having adiameter above 1000 Å.

The present invention is based on the finding that an unexpectedly longlived catalyst is obtained from the small change in pore sizedistribution. In another aspect of this invention, the distinctive poresize distribution is obtained by an improvement in the method of makingthe catalyst support In particular, the support is prepared by:

(a) treating a peptizable particulate solid comprising predominantlyalpha-alumina monohydrate by admixing the solid with an aqueous acidicsolution to a pH in the range of about 3.0 to 4.5;

(b) neutralizing at least a portion of the admixed acid by admixing intothe treated solid an aqueous solution of a nitrogen base containing anamount of base in the range of from about 0.6 to 1.0 equivalents perequivalent of said acid;

(c) shaping the neutralized or partially neutralized solid; and

(d) completing the support by drying and calcining the shaped solid at atemperature in the range of about 150° F. to 1700° F.

In another aspect of this invention, the back-neutralization isincreased in number of nitrogen base equivalents of peptizing acid, andthe calcination temperature is increased to produce a larger porecatalyst which has more metals capacity for resid conversion, than thecatalyst of the prior art. It is particularly useful with feedstocks ofcomparatively higher metals content.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the pore diameter distribution of the catalyst of thepresent invention

FIG. 2 (prior art) shows the pore diameter distribution of a prior artcatalyst.

FIG. 3 shows the temperature required to maintain 55% microcarbonresidue (MCR) conversion at 0.46 liquid hourly space velocity (LHSV)feed rate of a blend of one-third by weight Maya atmospheric resid andtwo-thirds by weight Arab heavy atmospheric resid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The catalytic process of the present invention is basically directed toresiduum feedstocks as opposed to gas-oil feedstocks. Residua typicallyhave greater than 10 ppm metals, whereas gas-oils nearly always haveless than 10 pm metals content. Thus, typical feedstocks for the presentinvention are crude oil atmospheric distillation column bottoms (reducedcrude oil or atmospheric column residuum), or vacuum distillation columnbottoms (vacuum residua). The metals are believed to be present asorganometallic compounds, possibly in porphyrin or chelate-typestructures, but the concentrations of metals referred to herein iscalculated as parts per million pure metal.

Alumina is the preferred support material of the catalyst used in theprocess of the present invention, although alumina may be combined withother refractory support materials such as silica or magnesia.

The alpha-alumina monohydrate preferably used in the present inventionis available from a variety of commercial sources, such as Catapal orVersal. It may also be prepared as described in Tamm '661.

The support material comprising alumina must have the previouslymentioned pore size distribution to give a catalyst in accordance withthe requirements of the present invention. The pore size distributionfor the alumina support used to form the finished catalyst issubstantially similar to the finished catalyst pore size distributionsince there is little change in pore size distribution upon impregnatingthe support with Group VIB and Group VIII metal compounds. Relativelypure alumina is available from several sources as spray-dried, amorphousor crystalline hydrate powders. These materials are suitable forextrusion when mixed with water only after the addition of an extrusionaid. Two commonly used aids are a strong mineral acid or a combustibleorganic lubricant. The former usually leads to high density extrudatesand the latter leads to pore size distributions containing substantialmicropore volume, neither of which is acceptable in a residuumdesulfurization catalyst support in accordance with the presentinvention. The patents of Tamm, previously incorporated herein, disclosea procedure by which such a material can be used to obtain a moderate tolow density alumina having greater than 97%, usually greater than 99%,of its pore volume in the micropore region. That is in the region ofpore diameters less than about 500 Å.

In the present invention the process of the Tamm patents is improved bya specific method of manufacture improvement which shifts the pore sizedistribution from 70% of the pore volume in pores having a diameter ofbetween 80 and 150 Å to a pore size distribution in which 70% of thepore volume is in pores having a diameter of between 110 and 190 Å. Aspointed out in Tamm '661, the acid treated particulate solid aluminamonohydrate is partially neutralized by admixing into the treated solidan aqueous solution of nitrogen base containing an amount of base in therange of from about 0.6 to 1.2 equivalents per equivalent of previouslyadded acid. This process is sometimes known as "back-titration". It isan aspect of the present invention that the back-titration is carriedout with a solution of nitrogen base, containing an amount of base inthe range of from about 0.6 to 1.0 equivalents per equivalent of saidpreviously added acid.

In order to produce an alumina support or carrier having a pore sizedistribution in accordance with that required by the present invention,the alumina must be treated with a suitable monobasic acid, preferablynitric acid, or its equivalent, as heretofore described (Tamm '661),e.g., hydrochloric, hydrofluoric and hydrobromic acids.

As was recognized the acid treated alumina is satisfactory for theproduction of a finished carrier substantially free of macropores.However, it is not satisfactory for the production of a catalyst carrierwith appropriate pore volume for use in the preparation of residuumdesulfurization catalyst. A satisfactory residuum desulfurizationcatalyst carrier and catalyst should have a pore volume of at leastabout 0.5 cc/gm, preferably at least 0.65 cc/gm. In general, the higherthe pore volume, provided that the micropore distribution and macroporecontent are satisfactory, the longer is the catalyst life. In order toachieve a useful pore volume and to provide a suitable microporedistribution as required for the finished carrier and catalyst, anappreciable fraction of the admixed acid in the treated feed must beneutralized with a nitrogen base which has been thoroughly admixed intothe feed by intensive mixing.

By "nitrogen base" as used herein is meant a base of the formula: R₃ Nand the corresponding hydroxide form, R₃ HNOH, wherein the R groups arethe same or different and are selected from the group consisting ofhydrogen and of alkyl groups having a carbon atom content in the rangeof from 1 to 3, inclusive. Aqueous ammonia is preferred.

The prior art recommends that "ordinarily, for each equivalent of theacid employed in the treatment, at least about 0.6 equivalents of thebase is required". The prior art contends that the use of a largerelative amount of the base for neutralization is increasinglybeneficial up to a point. Thereafter, the use of a larger relativeamount is undesirable. According to Tamm '661 excellent results in termsof the finished carrier are obtained, in general, when the relativeamount of the base in the aqueous solution per equivalent of the acid isin the range of about 0.6 to 1.2 equivalents, and when this ratio isabout 1.6, the resulting carrier is usually unsatisfactory.

It is the finding of the present invention, that for an improved highactivity resid catalyst, the relative amount of the base in the aqueousneutralization solution per equivalent of the acid should be in therange from about 0.6 to 1.0 equivalents, preferably more than about 0.55equivalents per equivalent of acid.

The nature of the mixture resulting from the neutralization of thetreated alumina varies, depending upon its volatiles content. It may bea flowable solid or a viscous paste. In the preferred form required foruse as an extrusion feed, it is a flowable solid having a volatilescontent in the range of from 50 to 70 wt. %. The term "volatile" as usedherein is the material evolved during the high temperature ≧900° F.drying. A variety of shaping methods may be employed for forming theprecursor of the catalyst carrier from the treated and neutralizedsolid. Preferably, the shaping is affected by extruding. In theproduction of the finished carrier, drying and calcining steps of thepresent method are in general carried out at temperatures in the rangefrom about 150° F. to 1700° F. The drying step is typically carried outin the range of from about 150° F. to 500° F. and following the dryingthe calcination is carried out in a dry or humid atmosphere at atemperature in the range of from about 500° F. to 1700° F., preferably1050° F. to 1700° F., most preferably greater than 1500° F.

The present method results in the production of moderate to low density,predominantly alumina, catalyst carriers having preferably greater thanabout 98% of their pore volume in the micropore region; and inparticular, having at least 70% of the total pore volume in pores havinga pore diameter in the range between 110 and 190 Å, less than 5% of thetotal pore volume in pores having a diameter above 500 Å, and less than2% of pores having a pore diameter above 1000 Å. Table I presents atypical distribution of the pore volume among the pore diameters in aprior art catalyst described by Tamm '661, '574, and '625. Table IIpresents a typical pore volume distribution amongst the pore diametersof a catalyst of the present invention.

Pore volume as described here is the volume of a liquid which isadsorbed into the pore structure of the sample at saturation vaporpressure, assuming that the adsorbed liquid has the same density as thebulk density of the liquid. The liquid used for this analysis was liquidnitrogen. The procedure for measuring pore volumes by nitrogenphysisorption is further laid out in D. H. Everett and F. S. Stone,Proceedinqs of the Tenth Symposium of the Colstrom Research Society,Bristol, England: Academic Press, March 1958, pp. 109-110.

                  TABLE I                                                         ______________________________________                                        PORE          CUM.       PORE VOL.                                            DIAMETER      PORE VOL.  (EST.)                                               (ANG.)        (%)        (CC/GM)                                              ______________________________________                                        1000.00       0.009      0.0001                                               900.00        0.029      0.0002                                               800.00        0.065      0.0005                                               700.00        0.119      0.0010                                               600.00        0.192      0.0015                                               500.00        0.295      0.0024                                               400.00        0.410      0.0033                                               300.00        0.717      0.0058                                               250.00        1.021      0.0082                                               240.00        1.111      0.0090                                               230.00        1.230      0.0099                                               220.00        1.436      0.0116                                               210.00        1.705      0.0137                                               200.00        2.129      0.0172                                               190.00        2.680      0.0216                                               180.00        3.548      0.0286                                               170.00        6.088      0.0491                                               160.00        12.180     0.0982                                               150.00        23.636     0.1905                                               140.00        39.950     0.3220                                               130.00        57.483     0.4634                                               120.00        71.144     0.5735                                               110.00        80.589     0.6496                                               100.00        87.513     0.7054                                                95.00        90.229     0.7273                                                90.00        92.480     0.7455                                                85.00        94.451     0.7614                                                80.00        96.096     0.7746                                                75.00        97.430     0.7854                                                70.00        98.426     0.7934                                                65.00        99.166     0.7994                                                60.00        99.708     0.8038                                                55.00        100.146    0.8073                                                50.00        100.430    0.8096                                                45.00        100.564    0.8107                                                40.00        100.640    0.8113                                                35.00        100.686    0.8116                                                30.00        100.535    0.8104                                                25.00        100.359    0.8090                                               ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        PORE          CUM.       PORE VOL.                                            DIAMETER      PORE VOL.  (EST.)                                               (ANG.)        (%)        (CC/GM)                                              ______________________________________                                        1000.00        0.007     0.0001                                               900.00         0.032     0.0003                                               800.00         0.090     0.0008                                               700.00         0.173     0.0015                                               600 00         0.254     0.0022                                               500.00         0.387     0.0034                                               400.00         0.595     0.0052                                               300.00         1.052     0.0092                                               250.00         1.621     0.0142                                               240.00         1.818     0.0159                                               230.00         2.063     0.0180                                               220.00         2.439     0.0213                                               210.00         2.900     0.0253                                               200.00         3.797     0.0332                                               190.00         6.357     0.0556                                               180.00        12.723     0.1112                                               170.00        26.368     0.2304                                               160.00        44.063     0.3850                                               150.00        58.600     0.5121                                               140.00        69.041     0.6033                                               130.00        77.690     0.6789                                               120.00        84.781     0.7408                                               110.00        90.186     0.7881                                               100.00        94.129     0.8225                                                95.00        95.594     0.8353                                                90.00        96.870     0.8465                                                85.00        97.970     0.8561                                                80.00        98.831     0.8636                                                75.00        99.476     0.8692                                                70.00        99.970     0.8736                                                65.00        100.311    0.8765                                                60.00        100.551    0.8786                                                55.00        100.722    0.8801                                                50.00        100.808    0.8809                                                45.00        100.829    0.8811                                                40.00        100.779    0.8806                                                35.00        100.688    0.8798                                                30.00        100.547    0.8786                                                25.00        100.338    0.8768                                               ______________________________________                                    

The hydrocarbon hydrodesulfurization catalysts of the present inventioncontain at least one hydrogenation agent, and preferably contain acombination of two such agents. The metals and/or the compounds of themetals, particularly the sulfides and oxides of Group VIB (especiallymolybdenum and tungsten) and Group VIII (especially cobalt and nickel)of the elements are in general satisfactory catalytic agents, and arecontemplated for use with substantially macropore-free carriers producedby the method of the present invention. The combinations of cobalt,nickel and molybdenum catalytic agents are preferred.

The catalytic agents required for the present catalyst compositions maybe incorporated into the calcined carrier by any suitable method,particularly by impregnation procedures ordinarily employed in generalin the catalyst preparation art. It has been found that an especiallyoutstanding catalyst is made when the alumina used not only has the poresize distribution required in accordance with the present invention, butalso wherein the catalyst is made by a single step impregnation of thealumina using a solution of a cobalt or nickel salt and aheteropolymolybdic acid, for example, phosphomolybdic acid.

The following examples illustrate the preparation of the catalyst of thepresent invention.

EXAMPLES Example A Preparation of the Catalyst Support

An alumina feedstock consisting of 60% Catapal alumina and 40% Versal250 alumina was peptized with 7.6% nitric acid, and back-neutralizedwith 71% ammonium hydroxide, 63% volatiles by weight were present.Specifically, 1260 gms of Catapal and 840 gms of Versal on avolatiles-free basis were maintained at a temperature between 130° F.and 140° F., mixed together with 228 gms of concentrated nitric acid and1515 gms of deionized water at about 150 cc/min. in a blender for 15minutes or until pasty. One hundred nine (109) gms of concentratedammonium hydroxide (58 wt. % ammonia hydroxide), was mixed with 1090 gmsof deionized water and added to the mixer at the rate of about 150cc/min. and then mixed for an additional 15 minutes. The volatilescontent was 63.6 wt. %. The paste temperature was 144° F. The paste wasextruded in a two-inch extruder, using a 0.039-inch cylindrical die Theextrudate was air-dried and heated in an oven at 250° F. for two hours.Then heated at 400° F. for two additional hours. The weight recoveredwas 1,958 gms. The dried extrudate was calcined for one hour at 1500° F.and an a ir rate of 1 cubic foot per hour of dry air. The particles hadthe following properties. Particle diameter 0.0322.increment.; particledensity: 0.8730 grams/cc; total pore volume: 0.8046 cc/gm; surface area:180 m² /gm. This support material was then impregnated with nickel andmolybdenum in the following manner. A mixture of molybdenum oxidedissolved in ammonium hydroxide was acidified with phosphoric acid to apH of 3.53, and nickel nitrate hexahydrate was added to a final pH of2.55. The catalyst was dried at 250° F. for two hours and at 400° F. forsix hours. It was then calcined with 20 cubic feet per hour of dry airfor four hours at 450° F., four hours at 750° F. and five hours at 950°F. The finished catalyst contained 8.12 wt. % molybdenum, 2.91 wt. %nickel, and 1.79 wt. % phosphorous. The median pore diameter was 154 Åwhich is larger than the prior art catalyst The surface area was 154 m²/gm. See FIG. 1.

Example B

The catalyst of Example A was compared with the analogously preparedcatalyst of the prior art (see Table I and FIG. 2 (prior art)--Tamm'574, '625, '661) in a standard life test. In this test, the conversioncatalyst was charged to a reactor under a layer of standard commercialdemetallation catalyst, and both catalysts were presulfided usingdimethyl disulfide. The layered catalyst system was then contacted witha feed blend containing 35 wt. % 650° F.+Maya and 65 wt. % 720°F.+Arabian Heavy residuum at 0.46 LHSV and 2200 psig total pressure andwith a 5000 SCF/bbl recycle hydrogen flow. The hydrogen partial pressurewas maintained above 1800 psig by use of a controlled bleed stream onthe recycle stream. The reaction temperature was controlled to maintain55% MCR conversion based on MCR content of the feed, where microcarbonresidue (MCR) is defined by ASTM D4530-85. The run was consideredfinished and the catalyst completely fouled when the reactiontemperature requirement exceeded 800° F. FIG. 3 shows the temperaturerequired to maintain 55% MCR conversion. According to the results shownin FIG. 3, the catalyst of this invention maintained useful activity fora significantly longer period of time than did the reference catalyst.

What is claimed is:
 1. A catalyst for the hydrodesulfurization of heavyoils, comprising an alumina support having:(a) a pore volume in therange of about 0.5 to about 1.1 cubic centimeters per frame, (b) aparticle density less tan 1.0, (c) at least 80% of said pore volume inpores having a diameter between 110 and 190 Å, (d) at least 70% of saidpore volume in pores having a diameter between 130 and 200 Å, (e) lesstan 5% of said pore volume in pores having a diameter above 500 Å, (f)less than 2% of said pore volume in pores having a diameter above 1,000Å, and a Group VIB component and a Group VIII component selected fromthe group consisting of the metals, oxides and sulfides of the elementsof Group VIB and VIII.